Process for the condensation of hydroxyl-containing organosilicon compounds using lithium hydroxide or lithium diorganosilanolate



United States Patent "ice 3,156,668 PRUCESS FOR THE CUNDENSATEON 0F HY-DRQXYL CCQNTAINING ORGANOSILICGN CQMFUUNBS lUSlNG LETHHUM HYDRGXIDE 0RLHTPJYUM DIQRGANUSXLANQLATE Ronald M. llilre, Chelmsford, Mass, assignorto Union Carbide Qorporation, a corporation of New Yorlr No Drawing.Filed Dec. 8, i959, Ser. No. 858,929 Claims. (Cl. Zed-46.5)

This invention relates to a process for producing organosiliconcompounds.

It is known that hydroxyl-containing organosilicon compounds representedby the formula:

i" 110 51K) R wherein R is a substituted or unsubstituted monovalenthydrocarbon group, R is an alkyl group or a hydrogen atom and n has avalue of at least one can be condensed in the presence of a catalyst(e.g. sulfuric acid or potassium silanolate) to produce a variety ofuseful diorganosiloxane products.

By way of illustration, it is known that those hydroxylcontainingorganosilicon compounds represented by Formula 1 wherein R and R havethe above-defined meanings and n has a value from 1 to 7 can becondensed to form cyclic diorgano-siloxanes (i.e. diorganosiloxanecyclic trimers to heptamers) which can be separated from the reactionmixture free of most of the monofunctional and trifunctional impuritiesthat often contaminate the hydroXyl-containing organosilicon compounds.These pure cyclic diorganosiloxanes can then be used in conventionalapplications wherein monofunctional and trifunctional impurities producedeleterious effects (e.g. in the production of gums for use in producingsilicone elastomers). However, the catalysts currently employed ineffecting the condensation of these hydroxyl-containing organosiliconcompounds also catalyze the equilibration of diorganosiloxanes. Whenequilibrium is reached in such equilibration reactions, the reactionmixture contains 648% by weight of the desired low molecular weightcyclic diorganosiloxanes and 82-94% by weight of higher molecular weightlinear diorganopolysiloxanes (oils or gums). The equilibriumconcentration of such low molecular weight cyclic diorganosiloxanes isconventionally increased above 18% by conducting the condensation in asolvent but, upon removal of the solvent from such reaction mixtures,the equilibrium concentration of these cyclic diorganosiloxanes revertsto 6-18% by weight unless the catalyst is also removed. Alternately,yields of the desired cyclic diorganosiloxanes higher than about 18% areconventionally obtained by continuously removing these cyclicdiorganosiloxanes from the reaction mixture by distillation operations.The higher molecular weight diorganopolysiloxanes are thereby caused todepolymerize continuously to maintain the equilibrium concentration ofthe desired cyclic diorganosiloxanes in the reaction mixture. Thenecessity for such distillation operations increases process costs andso constitutes an undesirable feature of such processes.

As a further illustration, it is known that those hydroxyl-containingorganosilicon compounds represented by Formula 1 wherein R and R havethe above-defined meanings and n has a value of at least 8 can becondensed to form diorganopolysiloxane oils and gums that can beemployed, for example, in producing silicone elastomers. However, aspointed out above, the catalysts currently employed in effecting thecondensation of these hydroxyl-containing organosilicon compounds alsocata- 3,155,653? Patented Nov. 10, 1964 lyze equilibration reactions andso 618% by weight of the desired diorganopolysiloxane oils and gums areconverted to lower molecular weight cyclic diorganosiloxanes (i.e.mostly diorganosiloxane cyclic trimers and tetramers). Consequently, theyield of the desired diorganopolysiloxane oils and gums are diminishedand the oils and gums contain 6-18% by weight of the low molecularweight cyclic diorganosiloxanes.

This invention is based on the discovery that lithium hydroxide andlithium diorganosilanolates catalyze the condensation ofhydroxyl-containing organosilicon compounds represented by Formula 1 butdo not catalyze the equilibration of diorganosiloxanes to a significantextent. This invention provides a process which involves condensinghydroxyl-containing organosilicon compounds represented by Formula 1 inthe presence of a catalytic amount of lithium hydroxide or a lithiumdiorganosilanolate.

The catalysts employed in this invention are lithium hydroxide andlithium diorganosilanolates which can be represented by the formula:

wherein R and n have the meanings defined for Formula 1 and R" islithium or hydrogen. Illustrative of these silanolates are: LiO[Me SiO]Li, LiO[Me SiO] OH,

.Lio[MeLio]..Li

Li[(C H SiO] H and the like. These silanolates can be produced by knownmethods (e.g. by mixing two moles of lithium hydroxide and one mole ofHO(Me SiO) H and heating the mixture at 50 C. for one hour to produceLiO Me SiO) Li.

The hydroxyl-containing organosilicon compounds employed in thisinvention are represented by Formula 1. Illustrative of theunsubstituted monovalent hydrocarbon groups represented by R in Formula1 are the alkyl groups (e.g. the methyl, ethyl and octadecyl groups),the cycloalkyl groups (e.g. the cyclohexyl and the cyclopentyl groups),the aryl groups (e.g. the phenyl, tolyl, xylyl and naphthyl groups), thearalkyl groups (e.g. the benzyl and beta-phenylethyl groups), theallsenyl groups (e.g. the vinyl, allyl and hexenyl groups) and thecycloalkenyl groups (eg the cyclohexenyl groups). Illustrative of thesubstituted monovalent hydrocarbon groups represented by R in Formula 1are the alkyl, cycloallryl, aryl, arallryl, alltenyl and cycloalkenylgroups containing as substituents one or more halogen atoms or amino,cyano, carbalkoxy, aminoalkylamino, hydroxyl or hydrocarbonoxy (e.g.alkoxy or aryloxy) groups. These substituents do not react to anysignificant extent during the condensation reaction. The groupsrepresented by R in Formula 1 preferably contain from 1 to 10 carbonatoms. Illustrative of the alkyl groups represented by R in Formula 1are the methyl, ethyl and propyl groups. In Formula 1 n can represent anaverage value in those cases where mixtures of hydroxylcontainingorganosilicon compounds are employed.

Typical of the hydroxyl-containing organosilicon compounds representedby Formula 1 are those that are more specifically represented by theformulae.

no S lO 11 Me a (3) no S iO c D C3 6 r HO SiO SiO H Me p R q 1\IIe VI'iHO SiO SiO O H Me n R q wherein n, p and q each have a value of at leastone, and R' is a methyl or an ethyl group. As used herein Me denotes themethyl group and Vi denotes the vinyl group.

The hydroxyl-containing organosilicon compounds employed in thisinvention can be produced by known processes. By one such known process,a diorganodialkoxysilane is hydrolyzed and partially condensed in amixture of a water and a solvent (e.g. ether). By another such knownprocess, a cyclic diorganosiloxane is reacted with steam at an elevatedtemperature and pressure.

In general amounts of catalyst that provide from 0.001 part to parts byweight of lithium per 100 parts by weight of the startinghydroxyl-containing organosiilcon compounds are useful in the process ofthis invention. Amounts of catalyst that provide 1 part to 2 parts oflithium per 100 parts by weight of the starting organosilicon compoundare preferred. Although other than the indicated amounts of catalyst canbe used, no commensurate advantage is gained thereby.

The process of this invention is advantageously conducted at atemperature from C. to 175 C. However, the process is preferablyconducted at a temperature from 90 C. to 150 C. Adherence to theindicated temperature ranges is generally desirable but not critical.

The process of this invention involves a condensation reaction thatproduces water as a byproduct and that can be represented by theskeletal equation:

When hydroxyl-containing organosilicon compounds represented by Formula1 wherein R is an alkyl group are employed condensation reactionrepresented by the following skeletal equation can also occur to producean alcohol as a byproduct:

However in the latter case, the reaction represented by Equation 7occurs concurrently and at a faster rate. The water or the water andalcohol produced as a byproduct is preferably continuously removed fromthe reaction mixture during the reaction by suitable means, e.g. byheating the reaction mixture at reduced pressure (preferably from 1 to10 mm. of Hg) at the above-mentioned preferred temperatures tovolatilize the water or Water and alcohol.

The hydroxyl containing organosilicon compounds and the catalyst can, ifdesired, be dissolved in an inert liquid organic compound in which theyare mutually soluble and the process of this invention can be conductedtherein. Suitable liquid organic compounds are ethers (e.g. diethylether and n-butyl ether), aromatic hydrocarbons (eg. xylene and toluene)and aliphatic hydrocarbons (e.g. ndecane). Amounts of these liquidorganic compounds from 10 parts to 1000 parts by weight per 100 parts byweight of the starting hydroxyl-containing organosilicon compounds areuseful but amounts of the liquid organic compounds from 50 parts to 200parts by weight of the starting hydroxyl-containing organosiliconcompounds are preferred. At the completion of the process, the liquidorganic compound can be removed from the desired diorganosiloxane by anysuitable means, eg. by heating the reaction mixture to a temperaturesufficiently elevated to volatilize the liquid organic compound.

At the completion of the process of this invention the catalyst can beremoved from the diorganosiloxane by any suitable means e.g. by washingthe diorganopolysiloxane with acidified water.

Those hydroxyl-containing organosilicon compounds that are representedby Formula 1 wherein R and R have the above-defined meanings and n has avalue from 1 to 7 are condensed according to the process of thisinvention to produce mixtures containing cyclic diorganosiloxanes havingthe formula:

(le n wherein R has the above-defined meaning and J has a value from 3to 7 and higher molecular weight linear diorganopolysiloxanes. When thecondensation of the lattor-mentioned hydroxyl-containing organosiliconcompounds is conducted in the above-mentioned solvents, yields of cyclicdiorganosiloxanes represented by Formula 9 as high as 40% are obtained.Owing to the fact that the catalysts employed in this invention do notcatalyze the equilibration of cyclic diorganosiloxanes represented byFormula 9 to form higher molecular weight diorganopolysiloxanes, theyield to these cyclic diorganosiloxanes is not reduced by such reactionswhen the solvent is removed. Continuous distillation of such cyclicdiorganosiloxanes from the reaction mixture is not necessary to obtainyields as high as 40%.

Those hydroxyl-containing organosilicon compounds that are representedby Formula 1 wherein R and R have the above-defined meanings and n has avalue of at least eight are condensed according to the process of thisinvention to produce linear diorganosiloxanes having the formula:

R RO s io R wherein R and R have the above-defined meaning and q has avalue of at least sixteen. Owing to the fact that the catalysts employedin this invention do not catalyze the equilibration of suchdimethylpolysiloxanes, these dimethylpolysiloxanes are producedessentially free of low molecular weight cyclic siloxanes (i.e. theycontain from 0% to 3% by weight of such cyclic siloxanes).

In the production of linear diorganopolysiloxanes represented by Formula10 according to the process of this invention, the initial product is anoil. As the process is continued the viscosity of the oil increasestill, in the case of alkoxy-containing hydroxyl-containing organosiliconcompounds, a stable alkoxy end-blocked diorganopolysiloxane oil isproduced. In the latter case, the process can be stopped at anintermediate point (e.g. by removing the catalyst) to obtain adiorganopolysiloxane oil containing both hydroxyl and alkoxyend-blocking groups. In the case of hydroxyl-containing organosiliconcompounds free of alkoxy groups, the final product is a gum but theprocess can be stopped at an intermediate point to produce a hydroxylend-blocked diorganopolysiloxane oil.

The diorganopolysiloxane oils produced in accordance with the process ofthis invention are preferably those represented by Formula 10 wherein Rand R have the above-defined meanings and has a value from 200 to 4000.These oils can be produced by conducting the process until the viscosityor any other conveniently measured property of the oil indicates thatthe desired molecular weight has been obtained and then removing thecatalyst by any suitable means (e.g. by washing the oil with water todissolve the catalyst).

The diorganopolysiloxane gums produced in accordance with the process ofthis invention are preferably those represented by Formula 10 wherein Rand R have the above-defined meanings and g has a value from 6000 to15,000. These gums can be produced by conducting the process until thehardness (as measured, for example, by a Miniature Penetrometer) or anyother conveniently measured property indicates that the desiredmolecular Weight has been obtained and then removing the catalyst by anysuitable means (e.g. by washing the gum with Water to dissolve thecatalyst).

Those diorganopolysiloxane oils produced in accordance with the processof this invention that contain hydroxyl end-blocking groups undergo agradual increase in viscosity owing to the condensation of thesehydroxyl groups, especially if the oils are exposed to elevatedtemperatures. These oils can be stabilized against such increases inviscosity by reacting the oils with trihydrocarbonhalosilanes (e.g.trimethylchlorosilane) in order to convert the hydroxyl groups to stabletrihydrocarbonsiloxy groups as illustrated by the equation:

On the other hand, it is often desirable to leave these hydroxyl groupsintact, e.g. when it is desired to react the oil with an alkyd resin inorder to modify the properties of the resin.

Alkoxysilanes can be condensed along with the hydroxyl-containingorganosilicon compounds represented by Formula 1 wherein n has a valueof at least eight according to the process of this invention. Suitablealkoxysilanes are those represented by the formula:

wherein R and R have the above-defined meanings and r has a value from 1to 3. Such cocondensations involve reactions that can be represented byEquation 8. These cocondensations are useful in producingdiorganosiloxanes containing functional groups uniformly spacedthroughout the siloxane chain or at the end of the siloxane chain. Byway of illustration, a hydroxy-containing dimethylpolysiloxane can becocondensed with methylvinyldiethoxysilane to produce a siloxanecontaining uniformly spaced vinyl groups according to the equation:

wherein at is an integer. The siloxane so produced can be cured throughthe vinyl groups to produce a silicone gum. As a further illustration,hydroxy-containing dimethylpolysiloxanes [e.g. HO(Me SiO) H] can be cocondensed with methyltriethoxysilane to produce a siloxane containinguniformly spaced ethoxy groups which can be hydrolyzed and condensed toconvert the siloxane to a silicone resin. As another illustration, ahydroxylcontaining dimethylpolysiloxane [e.g. HO(Me SiO) I-I] can becocondensed with gamma-hydroxypropyldimethylethoxysilane to produce asiloxane containing gamma-hydroxypropyl chain terminating groups.

Illustrative of the alkoxysilanes represented by Formula 12 are:methyltriethoxysilane, methylvinyldiethoxysilane,gamma-aminopropylmethyldiethoxysilane,beta-carbethoxyethylmethyldiethoxysilane, gammacyanopropylmethyldiethoxysilane,N-(beta-amino-ethyl)-gamma-aminoisobutylmethyldiethoxysilane,methyltriethoxysilane, trimethylethoxysilane andgamrna-hydroxypropyldimethylethoxysilane.

The diorganosiloxanes that are produced in accordance with the processof this invention are known compounds that are useful in a variety ofapplications. Thus the cyclic diorganosiloxanes can be converted to gumswhich can be used in producing silicone elastomers, thediorganopolysiloxane oils can be used as hydraulic fluids and thediorganopolysiloxane gums can be used in producing silicone elastomers.

The following examples illustrate the present invention:

Example I A mixture was formed containing 10 grams of HO(Me- SiO) H and0.2 gram of lithium hydroxide. The mixture was heated for 40 hours at150 C. to produce a dimethylpolysiloxane gum free of low molecularweight cyclic dimethylsiloxanes.

Example 11 A mixture was formed containing 3.5 grams of lithiumhydroxide and 175 grams of a silicone oil represented by the averageformula:

CaHs

' HO SiiO CaHs The mixture was heated for four days at C. to produce agum. The gum so produced parts by weight) was mixed with 35 parts byweight of finely divided silica, 12 parts by weight of an ethoxyend-blocked dimethyl polysiloxane, 0.2 part by weight of iron oxide and2.5 parts by weight of a solution of a peroxide curing agent. Thelithium hydroxide had not been removed from the gum. The mixture was binaged for four weeks, remilled, mold cured at 220 F. for 30 minutes andpostcured at 350 F. for four hours to produce an elastomer. The linearshrinkage during the postcure was 3.0% due to curing and thermalcontraction of the elastomer.

For comparison purposes, a catalyst-free dimethylpolysiloxane gumcontaining 12 wt.-percent of octamethylcyclotetrasiloxane was convertedto an elastomer by a process essentially the same as that describedabove. This elastomer underwent a 7% linear shrinkage during postcuredue to curing and thermal contraction of the elastomer andvolatilization of low molecular weight cyclic diorganosiloxanes. Thelower linear shrinkage of the former elastomer is due to the absence oflow molecular Weight cyclic diorganosiloxanes in the starting gum.

What is claimed is:

1. A process for condensing organosilicon compounds represented by theformula:

(MezSiO) zotMeViSiO) 0.0 0 H wherein R is a member selected from thegroup consisting of the unsubstituted monovalent hydrocarbon groups andthe substituted monovalent hydrocarbon groups wherein each substituentis a member selected from the group of the halogen atom, and the amino,hydroxyl, cyano, carbalkoxy, aminoalkylamino, alkoxy and arylcxy groups,R is a member selected from the group consisting of the alkyl groups andthe hydrogen atom and n has a value of at least one, which processcomprises condensing an organosilicon compound represented by saidformula in the presence of a catalytic amount of a compound selectedfrom the group consisting of lithium hydroxide and the lithiumdiorganosilanolates.

2. A process for condensing organosilicon compounds represented by theformula:

i HO SIiO R (R SiO) (2) wherein R has the above-defined meaning and phas a value from 3 to 7, which process comprises condensing anorganosilicon compound represented by Formula 1 in the presence of acatalytic amount of a lithium diorganosilanolate represented by theformula:

LiO SliO Li wherein R and n have the above-defined meanings to produce acyclic diorganosiloxane represented by Formula 2.

3. A process for condensing organosilicon compounds represented by theformula:

wherein R is an alkyl group, n has a value of at least eight and R is amember selected from the group consisting of the alkyl group and thehydrogen atom to produce linear diorganopolysiloxanes represented byformula:

wherein R and R have the above-defined meanings, and q has an averagevalue of at least sixteen which process comprises condensing anorganosilicon compound represented by Formula 1 in the presence of acatalytic amount of lithium hydroxide to produce a diorganopolysiloxanegum compound of groups represented by Formula 1.

4. A process for condensing organosilicon compounds represented by theformula:

| E are 5 Me n $H (fH -CHZ H O (Si O O E 43113 p a wherein R" is amethyl group, p and q each have a value of at least one and the sum of pand q has a value of at least eight to produce a gum, which processcomprises heating an organosilicon compound represented by said formulato a temperature from 25 C. to 175 C. in the presence of a lithiumdiorganosilanolate represented by the formula:

Me LiO S iO Li lite wherein n has a value of at least eight in an amountsufficient to provide from 0.001 to 10 parts by weight of lithium per100 parts by weight of the organosilicon compound to produce the gum.

6. A process for condensing HO(Me SiO) H wherein n has a value of atleast eight, which comprises heating HO(Me SiO) H at a temperature fromC. to 150 C. and at reduced pressure in the presence of sufficientlithium hydroxide to provide from 1.0 to 2.0 parts of lithium per partsby weight of the HO(Me SiO) H to produce a dimethylpolysiloxane gum.

7. A process for condensing HO(Me SiO) H wherein n has a value of atleast eight, which comprises heating HO(Me SiO) I-I at a temperaturefrom 90 C. to C. and at reduced pressure in the presence of LiO Me SiOLi to provide from 1.0 to 2.0 parts of lithium per 100 parts by weightof the HO(Me SiO) H to produce a dimethylpolysiloxane gum.

8. A process which comprises cocondensing (1) an organosilicon compoundrepresented by the formula:

If HO fiiH R wherein R is a member selected from the group consisting ofthe unsubstituted monovalent hydrocarbon groups and the substitutedmonovalent hydrocarbon groups wherein each substituent is a memberselected from the group consisting of the halogen atoms and the amino,hydroxyl, cyano, carbalkoxy, aminoalkylamino, alkoxy and aryloxy groups,R is a member selected from the group consisting of the alkyl groups andthe hydrogen atom and n has a value of at least eight and (2) analkoxysilane represented by the formula:

wherein R and R have the above defined meanings and r has a value from 1to 3, said cocondensation being effected in the presence of a catalyticamount of a member selected from the group consisting of lithiumhydroxyide and lithium diorganosilanolates.

9. The process of claim 8 wherein the alkoxysilane ismethyltriethoxysilane.

10. The process of claim 8 wherein the alkoxysilane ismethylvinyldiethoxysilane.

References Cited in the file of this patent UNITED STATES PATENTS2,438,478 Hyde Mar. 23, 1948 2,834,748 Bailey et al. May 13, 19583,017,385 Sprung et a1 Ian. 16, 1962 FOREIGN PATENTS 799,917 GreatBritain Aug. 13, 1958 570,580 Canada Feb. 10, 1959 OTHER REFERENCESKantor: J. Amer. Chem. Soc., 76 (1954), 5190. Grubb: J. Amer. Chem.Soc., 77 (1955), 1405. Hurd: J. Amer. Chem. Soc., 76 (1954), 249.

1. A PROCESS FOR CONDENSING ORGANOSILICON COMPOUNDS REPRESENTED BY THEFORMULA
 8. A PROCESS WHICH COMPRISES COCONDENSING (1) AN ORGANOSILICONCOMPOUND REPRESENTED BY THE FORMULA: HO-(SI(-R)2-H)N-R'' WHEREIN R IS AMEMBER SELECTED FROM THE GROUP CONSISTING OF THE UNSUBSTITUTEDMONOVALENT HYDROCARBON GROUPS AND THE SUBSTITUTED MONOVALENT HYDROCARBONGROUPS WHEREIN EACH SUBSTITUENT IS A MEMBER SELECTED FROM THE GROUPCONSISTING OF THE HALOGEN ATOMS AND THE AMINO, HYDROXYL, CYANO,CARBALKOXY, AMINOALKYLAMINO, ALKOXY AND ARYLOXY GROUPS, R'' IS A MEMBERSELECTED FROM THE GROUP CONSISTING OF THE ALKYL GROUPS AND THE HYDROGENATOM AND N HAS A VALUE OF AT LEAST EIGHT AND (2) AN ALKOXYSILANEREPRESENTED BY THE FORMULA: